REDUCTION OF DEVIATION OF FREQUENCY-CHARACTERISTICS OF SAW FILTERS BYMECHANICAL POLISHING OF ZNO FILM SURFACE

It was found that the surface acoustic wave (SAW) amplitudes in SAW fi lters made of ZnO films vary from filter to filter even when the cente r frequencies are the same and the deviation of amplitudes must be red uced. It was found also that the frequency and amplitude characteristi cs could be improved by mirror polishing of the ZnO film surface. In a n SAW filter with a ZnO/interdigital transducer (IDT)/glass substrate structure, periodic convex areas due to the thickness of the finger el ectrode of IDT and fine roughness were present on the device surface. As a result of investigating the influence of the surface structure on the amplitude deviation, it was found that the convex areas did not i nfluence the electromechanical coupling coefficient; but they reduced the acoustic velocity of SAW. In addition, it was clarified that the c onvex areas due to the finger electrode and fine roughness on the ZnO surface caused deviations in the acoustic velocity of SAW and reflecti ons of SAW, causing a deviation in the amplitude characteristics.